The present invention generally relates to a MIMO multiple transmission device and method.
In general, the more the communication data rate is increased, the more the reception errors occur. For example, if the data modulation system is changed from 2 bits/1 symbol QPSK (Quadrature Phase Shift Keying) to 4 bits/1 symbol 16QAM (Quadrature Amplitude Modulation) or 6 bits/1 symbol 64QAM, the data rate is increased, but the data error rate is also increased.
As one technology in which the relationship between the data rate and the data error rate is adequately controlled according to communication status, the AMC (Adaptive Modulation and channel Coding) is known, where the data modulation system and the channel coding rate are adequately controlled according to communication status.
FIG. 1 is a conceptual diagram of a general adaptive modulation and channel coding (AMC) system. A base station 100 transmits to a user #1 terminal 201 and a user #2 terminal 202 with the same transmission power. The user #1 terminal 201 located near to the base station 100 receives high receiving power and has good channel conditions. Accordingly, a high data rate modulation system (for example, 16QAM) and a high channel coding rate are selected for the user #1 terminal 201. The user #2 terminal 202 located far away from the base station 100 receives low receiving power and has bad channel conditions. Accordingly, a low data rate but low data error rate modulation system (for example, QPSK) and low channel data rate are selected for the user #2 terminal 202.
FIG. 2 is a chart showing combinations of data modulation systems and channel coding rates. In the direction (downward direction) shown by an arrow, the data rates are increased, but the data error rates are also increased. Accordingly, the better the channel conditions are, the lower is the combination of modulation system and channel selected in the chart. Conversely, the worse the channel conditions are, the higher is the combination of modulation system and channel selected in the chart. In practice, a table is previously prepared, in which SIR (Signal to Interference power Ratio) as an index of channel conditions corresponds to data modulation systems and channel coding rates. With reference to the table in accordance with a measured channel condition, an adequate combination of data modulation system and channel coding rate is selected to realize AMC.
As one technology for dealing with data errors, the hybrid ARQ (Automatic Repeat Request) is known. The ARQ is a combination of packet re-send request when detecting error by CRC (Cyclic Redundancy Check) and error channel demodulation by error correction coding (channel coding).
FIG. 3 shows procedures of a general hybrid ARQ system. At a transmitter side, CRC bit addition (Step S1) and error correction coding (Step S2) are performed. At a receiver side, error correction decoding (Step S3) and error detection using CRC bits (Step S4) are performed. If an error exists, a re-send request is sent to the transmitter side. If no error exists, the transmission (reception) is completed (Step S5).
FIG. 4 shows three processing types (a), (b) and (c) in the hybrid ARQ. In the type (a), if a packet P1 has a demodulation error, the packet P1 is discarded, and a packet P2 having the same contents is re-sent and demodulated again. In the types (b) and (c), if a packet P1 has a demodulation error, the packet P1 is not discarded but held, and the held packet P1 and a re-sent packet P2 are combined to generate a packet P3, which is demodulated. In the type (b), the same packet is re-sent and the packet combination is performed to improve reception SIR. In the type (c), the re-sent packet had been punctured with a different pattern, and the packet combination is performed to improve coding gain.
FIG. 5 shows a structure of one antenna transmission frame generating unit in which the above mentioned AMC and hybrid ARQ are employed. The transmission frame generating unit comprises a packet data block generator 101, a CRC adder 102, a channel encoder 103, a coding rate changer 104, an interleaver 105 and a data modulator 106, which are connected in series. The packet data block generator 101 generates a packet data block (referred to as “transport block” in 3GPP (3rd Generation Partnership Project)) as one re-sent unit for the hybrid ARQ. The CRC adder 102 adds CRC. The channel encoder 103 performs channel encoding. The coding rate changer 104 performs coding rate changing by rate matching (puncture, repetition), and controls the repetition pattern and puncturing when resending in the hybrid ARQ. The interleaver 105 performs interleaving between transmission streams (including interleaving between frequencies in OFDM (Orthogonal Frequency Division Multiplexing)). The data modulator 106 performs data modulation.
As one technology realizing large capacity high speed information communication, the MIMO (Multi Input Multi Output) multiple system is known. FIG. 6 schematically shows the concept of the MIMO multiple system. As shown in (a), in a transmitter side, data are serial-to-parallel converted (Step S11) and transmitted via plural transmitting antennas #1˜#N with the same frequency. In a receiver side, signals received at plural antennas #1˜#M are signal-separated (Step S12) and parallel-to-serial converted to recover the information. In the MIMO multiple system, since a large amount of different pieces of information can be transmitted at the same time, it is possible to drastically increase information bit rates. Data flow A˜D when two antennas are used is schematically shown in (b).
FIG. 7 shows two types of MIMO multiple systems. In one type shown in (a), two transmission data signals (transmission streams) #1, #2 are transmitted via transmitting antennas #1, #2, respectively. In another type shown in (b), transmission data signals (transmission streams) #1, #2 are weighted by w1,1, w1,2, w2,1, w2,2, and transmitted via the transmission antennas #1, #2 to obtain antenna beam patterns as shown in (b). The present invention can be applied to both. types.
FIGS. 8˜10 show some conventional technologies employing the AMC and the hybrid ARQ in the MIMO multiple system (for example see LGE, “Multiplexing Chain for MIMO System,” 3GPP TSG RAN WG1, R1-040259, Malagua, Spain, February 2004).
FIG. 8 is a first conventional example of a transmission frame generating unit in the MIMO multiple system. As shown in (a), the transmission frame generating unit has a transmission stream #1 comprising a packet data block generator 101-1, a CRC adder 102-1, a channel encoder 103-1, a coding rate changer 104-1, an interleaver 105-1 and a data modulator 106-1, which are connected in series. The transmission frame generating unit has another transmission stream #2 comprising a packet data block generator 101-2, a CRC adder 102-2, a channel encoder 103-2, a coding rate changer 104-2, an interleaver 105-2 and a data modulator 106-2, which are connected in series. The transmission streams #1 and #2 are arranged in parallel. This transmission frame generating unit has features as shown in (b).
FIG. 9 is a second conventional example of a transmission frame generating unit in the MIMO multiple system. As shown in (a), the transmission frame generating unit, comprises a packet data block generator 101, a CRC adder 102, a channel encoder 103 and a coding rate changer 104. After these functions, the data stream is separated by a serial-to-parallel converter 107 into two streams #1 and #2, which have interleavers 105-1, 105-2 and data modulators 106-1, 106-2, respectively. This frame generating unit has features shown in (b).
FIG. 10 is a third conventional example of a transmission frame generating unit in the MIMO multiple system. As shown in (a), the transmission frame generating unit comprises a packet data block generator 101, a CRC adder 102 and a channel encoder 103. After these functions, the data stream is separated by a serial-to-parallel converter 107 into two streams #1 and #2, which have coding rate changers 104-1, 104-2, interleavers 105-1, 105-2, and data modulators 106-1, 106-2, respectively. This frame generating unit has features shown in (b).
The above mentioned conventional examples shown in FIGS. 8˜10 have problems discussed below.
In the MIMO multiple system, each transmission stream has different channel conditions, and therefore the AMC can be separately performed per each transmission stream to obtain better reception properties (throughput, packet error rate) than common transmission stream processing. With regards of this point, the first conventional example shown in FIG. 8 and the third conventional example shown in FIG. 10 are satisfactory, but the second conventional example shown in FIG. 9 does not allow the channel coding rate change to be separately controlled per transmission stream.
In the MIMO multiple system, the channel coding and the hybrid ARQ over individual transmission streams are preferable from the viewpoint of increasing the diversity effect at channel decoding. With respect to this point, the second conventional example shown in FIG. 9 and the third conventional example shown in FIG. 10 are satisfactory, but the first conventional example shown in FIG. 8 cannot realize the diversity effect.
The larger the packet data block size becomes, the larger the wastefulness in resending a packet in response to reception error becomes with respect to this point, the second conventional example shown in FIG. 9 and the third conventional example shown in FIG. 10 are disadvantageous.
Further, when the channel coding speed is fast, the work load in the receiver side becomes heavy. With respect to this point, the second conventional example shown in FIG. 9 and the third conventional example shown in FIG. 10 are disadvantageous.